1. Field of the Invention
The invention relates to the preparation of enriched reaction mixtures containing the alkaline earth metal salts of 2,2'-oxydisuccinic acid by a process which removes the salt of alkaline earth metal malates.
2. Related Art
2,2'-oxydisuccinic acid (ODS) and salts thereof are useful as sequestering agents and detergent builders. A disadvantage of ODS and its salts as detergent builders is that they may be relatively expensive to prepare.
U.S. Pat. No. 3,128,287 to Berg discloses a preparation of ODS salt by admixing maleic acid with an excess of hydroxide of calcium, barium, magnesium or strontium in the presence of water, then heating the reaction mixture from about one day to about one month at temperatures ranging from 50.degree. C. to reflux temperatures. The process yields a mixture of malic acid and ODS. Berg's Example I teaches the preparation of ODS, wherein the aqueous mixture of maleic anhydride and calcium hydroxide is reacted at reflux (100.degree. C.) for 4 days. Subsequently, ODS salt is isolated from the product containing ODS and malic acid salts.
U.S. Pat. No. 3,635,830 to Lamberti et al., discloses a process for the preparation of ODS based on the process of Berg. The patent teaches separation/purification of two diastereoisomeric forms of ODS obtained by the Berg process. The patent also discloses detergent compositions comprising ODS or salts thereof as detergent builders.
U.S. Pat. No. 5,030,751 to Lamberti discloses methods of preparing mixed salts of ODS and carboxymethyloxysuccinic acid.
U.S. Pat. No. 4,959,496 to Crutchfield discloses a process for preparing ether carboxylates and precipitating and recycling unreacted starting materials by reducing the pH to 4.5 to 5.5.
Japanese patents JP 4112849 and JP 4112850 disclose preparation of metallic salts of ether carboxylates by the addition of maleic acid or maleic anhydride to an aqueous mixture of an alkali metal salt of a hydroxycarboxylic acid and alkaline earth metal carbonate.
A workable and cost-efficient production of ODS salt must be directed towards optimizing the process conditions in ways which improve yields of the ultimate product without increasing expense. There have been different approaches to the problem of producing ODS at a lower cost. However, none of these approaches has been completely satisfactory.
Accordingly, it is an object of the present invention to provide a process which ultimately produces the alkaline earth metal salts of ODS in high yields by enriching the ODS content of the reaction mixture.
This and other objects and advantages will appear as the description proceeds.